In a CDMA radio communication system, a system to perform downlink high-speed packet transmission to users using a channel such as DSCH (Down link Shared CHannel) is proposed so that a base station (BS) downloads high-volume data to a communication terminal apparatus (TS) in a short time. This system will be explained using FIG. 1 below. FIG. 1 shows a configuration of a conventional radio communication system.
In FIG. 1, suppose base station apparatus 11 is currently conducting bi-directional radio communications with communication terminal apparatuses 21 to 23 using a communication channel (DPCH). In this case, communication terminal apparatuses 21 to 23 send information indicating the channel quality of the downlink to base station apparatus 11. The information indicating the channel quality includes SIR, etc.
Base station apparatus 11 sends packet signals to a communication terminal apparatus (e.g., communication terminal apparatus 21) which is selected based on the channel quality, etc. using DSCH. However, since high-speed packet transmission involves large transmit power and causes interference with other stations, this conventional base station apparatus adopts a time-division system and sends a packet signal to only one station at a time.
Here, the CDMA radio communication system may use adaptive array for the purpose of reducing interference. Adaptive array is a system to carry out transmission with directivity by mounting an array antenna made up of a plurality of antenna elements on a base station apparatus and sending transmission signals multiplied by complex coefficients (hereinafter referred to as “weights”).
Using adaptive array for downlink high-speed packet transmission reduces interference, and therefore use of adaptive array is expected to allow downlink high-speed packet transmission to be carried out to a plurality of users simultaneously.
However, in a CDMA radio communication systems using adaptive array, no method has been disclosed so far as the method capable of effectively performing downlink high-speed packet transmission.